Spatiotemporal patterns and environmental correlates of suicide seasonality in Brazil

Suicide exhibits a consistent seasonal pattern worldwide, peaking in late spring and early summer in both hemispheres. Yet, the biological mechanisms and environmental triggers underlying this temporal pattern remain poorly understood. Most studies have focused on temperate regions, while few have examined tropical or equatorial zones or conducted detailed, latitude-stratified analyses. Additionally, methodological inconsistencies limit cross-regional comparisons and contribute to conflicting findings. We analyzed monthly suicide data (2010-2019) from 5259 Brazilian municipalities, integrating sociodemographic, geographic, and climatic variables. Seasonal patterns and long-term temporal dynamics across variables were evaluated using Cosinor models, ARIMA forecasting, Granger causality, machine learning, and robust regressions. We confirmed a significant seasonal rhythm in suicide rates, with peaks near the summer solstice (December) and troughs in winter (June), particularly below -20° latitude, closely tracking photoperiod variation. Suicide rates and seasonal amplitude increased toward southern latitudes, indicating a latitudinal cline. Suicide rates were significantly associated with social-solar time misalignment (dGMT), with higher rates observed in western time zones. Regression models identified photoperiod, dGMT, urbanization, and Human Development Index as significant predictors, with urbanization inversely related to suicide. Although socioeconomic development correlated with suicide rates at the national level, this association did not persist within the seasonal region, likely reflecting underlying socioeconomic disparities between Brazil's geographic regions. Together, these findings highlight a latitudinal gradient in suicide seasonality in Brazil and suggest that circadian misalignment driven by photoperiod and social time structures may play a key role in shaping suicidal behavior.